Denmark has introduced extra border controls. Politicians who support the move say it\'s to stop the influx of illegal immigrants which include criminals. The plan\'s opponents say it\'s the start of a potentially dangerous, xenophobic trend. Brussels says it\'s against the spirit of the European Union\'s Schengen agreement which allows free movement across Europe\'s internal borders and may even breach the letter of the treaty. It all fits into a wider debate about the future of immigration into and around the EU.